The present disclosure relates to a micro-structured reference element which changes the value of an electrical property on the basis of temperature for sensors which is thermally coupled to a substrate but which is electrically insulated from said substrate. The disclosure also relates to a sensor arrangement, comprising a reference element according to the disclosure and also a micro-structured sensor element having an electrical property which changes its value on the basis of temperature. In addition, the disclosure relates to a method for operating a temperature sensor.
Semiconductor sensors can detect temperature changes, for example as a result of infrared radiation, using the electrical properties of semiconductor components such as diodes. To this end, they usually use reference elements which are kept to the temperature of the sensor substrate by design measures. Difference formation for the sensor signals and the reference signals allows even small changes in the temperature or in the infrared radiation to be sensed with a comparatively large offset signal. It is also possible to eliminate spurious signals caused by the electronics themselves. Such spurious signals may be a drift as a result of a measurement electronics temperature which has changed during operation.
On the basis of the design principle, the sensor elements should be electrically insulated and thermally decoupled from the other elements which are on the sensor substrate and from the substrate itself. By contrast, the reference elements should be electrically insulated, but thermally coupled to the substrate.
The sensor elements can be thermally decoupled by cavities, that is to say hollow spaces beneath the sensor elements. Thus, DE 10 2006 028 435 A1 discloses a sensor, particularly for spatially resolved detection, which has: a substrate, at least one micro-structured sensor element with an electrical property which changes its value on the basis of temperature, and at least one membrane above a cavern, wherein the sensor element is arranged on the underside of the at least one membrane and wherein the sensor element is arranged on the underside of the at least one membrane and wherein the sensor element is contacted by means of supply lines which run in, on or under the membrane. In particular, there may be a plurality of sensor elements in the form of diode pixels in a monocrystalline, epitaxially produced layer. The membrane may have suspension springs produced in it which hold the individual sensor elements elastically and so as to provide insulation.
The electrical insulation but thermal coupling of reference elements in the sensors described at the outset is usually achieved by virtue of the cavity beneath the reference element being omitted. As a result, the element is thus directly linked to the substrate. The electrically conductive connection between the substrate and the reference element is achieved by additional dopings, for example by a p-doped layer between two n-doped layers. A drawback of this, however, is the changed electrical properties of the reference element, since the additional doping means that said reference element is no longer equivalent to the sensor elements.